This invention relates to a photosensitive body for electrographic apparatus.
An electrographic apparatus which makes use of a mesh-shaped photosensitive body has heretofore been proposed. In such electrographic apparatus, the mesh-shaped photosensitive body is of four layer construction composed of an electrically conductive substrate having a number of openings, a photosensitive layer coated on one side of the substrate, an insulating layer coated on the other side of the substrate and an electrically conductive layer coated on the insulating layer. The mesh-shaped photosensitive body is uniformly charged and then exposed to a manuscript image so as to produce, on the mesh-shaped photosensitive body, a first electrostatic latent image corresponding to the manuscript image. Subsequently, a flow of corona ions is modulated on the basis of the first electrostatic latent image to produce, on an electrostatic record sheet, a second electrostatic latent image corresponding to the first electrostatic latent image. The second electrostatic latent image produced on the electrostatic record sheet is developed and fixed to obtain a visible image.
In such electrographic apparatus, in the case of producing, on the electrostatic record sheet, the second electrostatic latent image, a corona discharge electrode for emitting a flow of corona ions must be opposed through the mesh-shaped photosensitive body to the electrostatic record sheet. For this purpose, the mesh-shaped photosensitive body is required to be held at its margin on the outside of an effective picture surface range, for example, to be held at its end edges.
A drum-shaped photosensitive body has also been proposed in which a mesh-shaped photosensitive body is wound around a drum-shaped supporting frame and firmly secured thereto.
In this case, however, since the photosensitive body is of a mesh-shaped one, it is difficult to handle it. In addition, in the case of winding the mesh-shaped photosensitive body around the drum-shaped supporting frame, at first the mesh-shaped photosensitive body must be temporarily fastened to the drum-shaped supporting frame and then the end edges of the mesh-shaped photosensitive body must be pulled under tension so as to remove wrinkles existing thereon and subsequently the mesh-shaped photosensitive body must be permanently secured to the drum-shaped supporting frame, thereby involving very troublesome operations for the purpose of securing the mesh-shaped photosensitive body to the drum-shaped supporting frame.
It has also been proposed to secure a mesh-shaped photosensitive body to a drum-shaped supporting frame with the aid of a thin plate-shaped frame which is bonded with the end edge of the mesh-shaped photosensitive body and secured to the drum-shaped supporting frame by means of screws.
An attempt has also be made to provide a drum-shaped supporting frame composed of a pair of spaced apart supporting discs and to provide between these supporting discs an intermediate disc which is arranged movably in the axial direction of the drum-shaped supporting discs. In this case, thin plates bonded to the end edges of the mesh-shaped photosensitive body are secured to both the outer periphery of the intermediate disc and the outer periphery of one of the pair of the supporting discs and then the intermediate disc is displaced toward the other supporting disc such that the drum-shaped photosensitive body becomes spread under tension around the discs.
In all of these prior art mesh-shaped photosensitive bodies, the side edges or end edges of the mesh-shaped photosensitive body are bonded with the thin plate. As a result, if a bonding agent becomes irregular in thickness or if the mesh-shaped photosensitive body is not flat in the case of bonding the thin plate therewith, the photosensitive body tends to produce wrinkles when it is formed into a drum-shape, thus rendering the spreading operation very difficult.
Another attempt has been made to provide a groove formed along the outer periphery of a pair of spaced apart supporting discs for constituting a drum-shaped supporting frame. The supporting discs are surrounded by a mesh-shaped photosensitive body and then against the groove is urged a resilient ring such that the mesh-shaped photosensitive body becomes spread under tension in a closely tight manner. In this case, an electrically conductive substrate of the mesh-shaped photosensitive body is composed of a wire mesh formed of a wire having a diameter of 30 to 50.mu. or is composed of an etched foil having a thickness on the order of 30 to 50.mu.. Such kind of wire mesh or etched foil has no flexibility which is sufficient to be deformed when it is spread under tension around the discs. As a result, it is impossible to spread under tension the photosensitive body around the supporting discs.
The drum-shaped photosensitive body composed of the mesh-shaped photosensitive body secured directly or through the thin plate to the drum-shaped supporting frame by means of the screws requires a plenty of operating time in the case of replacing the mesh-shaped photosensitive body by a new one or in the case of assembling it. In addition, in the above described various kinds of drum-shaped photosensitive bodies, the mesh-shaped photosensitive body is directly or through the thin plate secured to the supporting discs for constituting the drum-shaped supporting frame, so that there is a risk of the mesh-shaped photosensitive being wrinkled by the difference between the thermal expansion of the mesh-shaped photosensitive body and that of the drum-shaped supporting frame due to change in the surrounding temperature.